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Mitch Johnson
 Post subject: Testing Specific Gravity
PostPosted: Thu Feb 03, 2011 5:27 pm 
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How many of you out there test your tops for specific gravity. Is it a waste of time or does it yield some useful info? What are your methods if you do? I was shown a way to do it and I know it's done in the violin world sometimes. Just curious if anyone's doing it.
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Ti-Roux
PostPosted: Thu Feb 03, 2011 5:47 pm 
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It's pretty simple, and you can find density and humidity level at the same time.

Take a scrap that comes from your top. Take the precise volume Witdh x lenght x height. Mesure the weight. Then cook the piece to dry it completly, and mesure it again.

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Alain Moisan
PostPosted: Thu Feb 03, 2011 6:53 pm 
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Hi Mitch,

I'm not sure what you mean by 'gravity'. Could you explain what you have in mind?

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Zach Ehley
PostPosted: Thu Feb 03, 2011 7:47 pm 
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Specific gravity is density with 1 equalling pure water as the reference.

Petros has some listed on their site. General numbers at that. http://www.petrosguitars.com/woods.htm
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Alain Moisan
PostPosted: Thu Feb 03, 2011 10:50 pm 
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ok if you see it in the way that specific gravity is another way of expressing density, than yes, many of us care a lot about that. We just tend to stick to the more popular ratio of mass/volume.

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wbergman
PostPosted: Fri Feb 04, 2011 2:47 pm 
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If you do your volume measure in cubic centimeters and your weight in grams, then divide weight by volume, don't you get specific gravity without further conversion? You would do this on the wood as it is, without toasting it.
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Jim Watts
PostPosted: Fri Feb 04, 2011 2:55 pm 
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wbergman wrote:
If you do your volume measure in cubic centimeters and your weight in grams, then divide weight by volume, don't you get specific gravity without further conversion? You would do this on the wood as it is, without toasting it.

You do if your water density is actually 1, but the density of water varies with temperature, which is why a temperature is required for specific gravity as Todd pointed out.
The differnce between g/cc and specific gravity is moot for our work.

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Alain Moisan
PostPosted: Fri Feb 04, 2011 3:01 pm 
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Jim Watts wrote:
The differnce between g/cc and specific gravity is moot for our work.


I would tend to agree with that. It's not like we're doing nuclear science here...

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Alain Moisan
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